There has been little in the structure and shape of conventional twist drill during the past 100 years or more following its birth; with the continuous development of science and technology and mushrooming of new materials, higher requirements are imposed on solid drilling. However, conventional twist drills suffer from the following main problems:
1. Values of front angles of different points on the main cutting edge vary significantly and the front angles become negative around the drill core, leading to poor cutting conditions.
2. The chisel edge is too long with a very large cutting edge angle, which is a very large negative front angle, leading to poor cutting conditions. Hence, the axial resistance is large and the centering is not good.
3. The main cutting edge is long, the cutting is wide, the chips roll into wide spiral chips, the space occupied is large, making it difficult to remove the chips and for the cutting fluid to flow in.